The use of toxic, corrosive and explosive polyatomic gases is common to microelectronic and electro-optic thin film fabrication processes, such as chemical vapor deposition, epitaxy, ion implantation and doping. The polyatomic gases are one convenient source of a desired elemental species of interest. Safety issues require extreme care in the handling, storage and use of such toxic polyatomic gases at considerable extra cost to the end users. Limits on the maximum amount of toxic gas stored in a given location introduce additional operating costs due to the need for frequent gas bottle replacement on a given apparatus in a manufacturing enviroment. Finally, total dose limitations received by workers over a given time restrict the scheduling of workers in a work week where exposure to toxic chemicals occurs. Thus, for example, exposure to arsenic and its compounds should not exceed 0.5 mg/(Meter).sup.3 over a forty hour work week.
The volatile nature of liquid and gaseous forms of dangerous chemicals makes their containment and control especially problematic. If a leak should ever occur, the danger spreads quickly over a wide area. Special gas and liquid storage facilities, and special gas handling lines and regulators are all used in conventional toxic chemical support technology. Toxic gas monitoring equipment, including audible and visual alarms, must be used should an inadvertent release of dangerous gas or liquid ever occur. Finally, evacuation of manufacturing personnel from the entire manufacturing facility is required when a dangerous gas release occurs, not just the immediate vicinity of the toxic gas leak because only ppm or ppb levels are dangerous. This evacuation requirement involves additional cost and down time.
Direct and rapid control of dangerous species generation is the lynchpin of the present invention. This is to be compared to prior art furnace technology and downstream microwave plasma dangerous gas generation methods. See, for example, "MOCVD Growth of InP Using Red Phosphorous and a Hydrogen Plasma" by Masami Naitoh and Masayoshi Umeno, Japanese Journal of Applied Physics 26, 1538-1539 (1987). Like Naitoh and Umeno, our approach places the dangerous gas generation source inside a vacuum chamber safe from the immediate manufacturing enviroment. The approach of the present invention is distinguished from the prior art by its use of photon, electron or ion beam impingement on the solid target to produce the elemental species of interest, and by the use of refractory metal or ceramic foam-like structure to contain the dangerous elemental containing species in the pores.